In a portable electrical instrument or similar apparatus high-efficiency operation is axiomatic, especially if such instrument or apparatus derives required power from a DC voltge source such as a battery. Additionally, in electrical instruments or similar apparatus, it is essential to high efficiency operation to maintain a constant output voltage over a wide range of source voltage variation.
Prior art portable electrical instruments as well as standard electrical instruments have included circuits to improve the efficiency of operation. For example, a discussion concerning class-C oscillators and the difficulty of combining high efficiency within a satisfactory degree was presented at the International Convention on Transistors and Associated Semiconductor Devices, May 25, 1959; see The Institution of Electrical Engineers Paper No. 2978E, February 1960, "TRANSISTOR SINEWAVE LC OSCILLATORS" by P. J. Baxandall. However, omitted therefrom is the ability to maintain a constant output voltage over a wide range of source voltage variation while maintaining good power conversion efficiency.